The present invention relates to a method and a device for stimulating the accommodation of at least one eye of a subject. In particular, the present invention thereby offers a particularly reliable option for determining a set of ophthalmological data of at least one eye of the subject and, in particular, for measuring the refractive error of the subject and for establishing an appropriate optical correction.
Automated refractors or aberrometers are used ever more frequently for determining a possible refractive error of an eye patient or a customer (referred to as subject below) and for establishing the required optical correction (determining the refraction). By way of example, the prior art includes automated refractors which use simulated eye charts and—analogous to a phoropter—place different powers in front of the subject for subjective refraction and for subjective visual acuity determination. In respect of an automated refractor, reference is made in an exemplary manner to Allergan Humphrey: Das Humphrey-Refraktometer [The Humphrey refractometer] (July 2012).
Objective refraction, which is measured by means of a physical arrangement and determined by the refractive properties of the eye (in particular including the cornea, the lens and the vitreous humor), should be distinguished from subjective refraction, which requires information from the subject regarding the perceived image sharpness.
To this end, as is described in “K. Nicke and S. Trumm: Brillengläser der Zukunft—Schritt 3 Der DNEye Scanner [Spectacle lenses of the future—step three: the DNEye scanner], Der Augenoptiker, June 2012”, e.g. so-called virtual targets based on optical images are projected into the eye of the subject, by means of which the accommodative states of the eye can be controlled. According to the prior art, this image is realized, in particular, by one or more spherical lenses. A conventional virtual target in this case represents, in particular, an optical imaging system which generates spherical wavefronts emanating from virtual object points such that said wavefronts are incident on the eye of the subject. As a result, the subject has the (virtual) impression of a real object at a specific distance. Ideally, the apparent distance of the depicted object from the eye of the subject is set by the spherical curvature, i.e. the radius of curvature of the wavefronts impinging on the eye. By changing the imaging system of the virtual target, in particular by changing the radius of curvature of the wavefronts impinging on the eye, it is possible to stimulate the eye to accommodate to the different object distances within the physiological possibilities thereof. As a result, the eye can be examined at different accommodative states which, in particular, can be set in a targeted manner and/or the boundaries of the accommodative power of the eye can be gauged.
Conventionally, instruments such as automated refractors and aberrometers perform eye-optical measurements or ophthalmic examinations in the far accommodative state, i.e. in the case of relaxed ciliary muscles. To this end, a virtual target is generated with the aid of at least one spherical lens, which represents an image of an object in the eye of the subject. Here, backlit diapositives are usually used as an object. The position of the at least one lens in relation to the slide and, in the case of a plurality of lenses, also in relation to one another renders it possible in this case to control the image for the limiting case even in such a way that the eye can no longer accommodate to the image (i.e. the virtual object) due to the large virtual object distance, i.e. the image is only identified out of focus in all directions and the aforementioned relaxed state of the eye sets in. This process is also often referred to as “haziness” and the corresponding relaxed state as “hazy state”. In order to cause such haziness in a subject, it is necessary to generate an image which is sufficiently beyond the stronger positive principal meridian. This is achieved, independently of the type of refractive error, in a simple manner by the use of lenses with a suitable spherical power.
Eye-optical measurements or ophthalmic examinations for close up, i.e. in the near accommodative state, are comparatively more difficult and less precise. This is firstly due to the fact that although a specific optical distance can be simulated with the aid of a virtual monocular target, other factors influencing the accommodation mechanism of the eye, such as e.g. the binocular disparity (different retinal images of the two eyes) and/or additional information from the scene (location and size of the object relative to other objects in the scene), remain unaccounted for. Secondly, a successful near measurement using a virtual target assumes that the subject also in fact accommodates during the measurement, i.e. that he attempts to see the target in focus.
It is for this reason that the accommodation power in the near-field region (i.e. in the case of a close-up view) which the eye would apply if this were a real target at the corresponding distance often cannot be simulated exactly with the aid of a virtual monocular target as is used in conventional aberrometers and automated refractors. Therefore, an objective refractive measurement only based on a predetermined virtual distance (of the target) for the accommodative state which is present when looking in this distance can be afflicted with significant errors.